Perfluoroelastomers are used where high temperature and/or chemical resistance are required in rubber parts, as in seals. These materials are typically crosslinked through small amounts of curesite monomers incorporated into the polymer chains to provide reactive crosslinking sites. However, for some uses, crosslinking using added chemicals is not necessarily desirable, since it may lead to outgassing of low molecular weight species from the crosslinked polymer, particularly at high temperatures, which can lead to chemical contamination of "clean" environments.
Perfluoroelastomers may also be cured by exposing them to ionizing radiation, which does not deliberately introduce new chemical species into the polymer. However, exposure to the radiation often results in relatively unstable groups being produced in the crosslinked perfluoroelastomer. It has now been found that fluorination destroys many of these unstable groups, resulting in a product with relatively low outgassing.
The fluorination of perfluorinated thermoplastics to remove "impurities" or relatively unstable groups is known, see for instance U.S. Pat. Nos. 4,675,380, 4,687,708 and 4,743,658. Partially fluorinated polymers have also been treated with fluorine to form a perfluorinated polymers, see U.S. Pat. No. 4,948,844. It is believed that none of these patents involve crosslinked polymers.